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Ratzilla: Ancient giant rodent chomped like a crocodile

An immense, bison-sized rodent that lived in southern South America about 3 million years ago may have used its thicker-than-your-thumb front teeth much like a modern-day elephant uses its tusks, a new study suggests. Known only from its 53-centimeter-long skull and described less than a decade ago, Josephoartigasia monesi is the largest fossil rodent yet discovered and may have weighed a metric ton (see artist’s conception above). Now, researchers using sophisticated software (the same sort employed to analyze stresses in aircraft parts) have estimated the bite forces the creature might have generated when it chewed. First, the scientists used a CT scanner to create a detailed model of the fossil skull; then they added a model of a lower jaw scaled up from a chinchilla, a close modern-day relative. Simulations suggest that at the rearmost tooth in the jaw, J. monesi’s bite forces measured about 4165 newtons, or about three times higher than those estimated for tigers and midsized crocodiles, the team reports online today in the Journal of Anatomy. At the tips of the creature’s ever-growing front teeth, bite force likely measured only about 1400 newtons. Yet for some inexplicable reason, the researchers say, those front teeth are apparently strong enough to take three times the stress produced by that bite force—a sign that the megarodent may have been using its chompers for something other than chewing. It’s possible that J. monesi used its front teeth to dig up roots, to defend itself against predators, or during fights for territory or for mates, just as modern-day elephants do, the researchers suggest. Future analyses of microwear patterns on the creature’s teeth may provide better insights into Ratzilla’s dietary habits.

*Correction, 6 February, 11:22 a.m.: This article has been revised to clarify the region of South America where the fossil skull of this creature was found.